The invention concerns a closed-loop control device for controlling at least one control value of at least one tempering circle of a tool of a molding machine with the features of the preamble of claim 1 and/or with the features of the preamble of claim 7 and a tempering device with such a closed-loop control device and a method for controlling the tempering circle.
The at least one tempering circle comprises a feed conduit by means of which the tool to be tempered is fed with tempering medium with a determined feed temperature and with a determined flow rate. The tempering medium is lead away from the tool by means of a return conduit. The tempering circle is formed by the feed conduit, the tempering conduit in the tool and the return conduit and can be designed open or closed. The tempering circle additionally comprises yet at least one valve and a sensor for adjusting and monitoring the flow of the tempering medium in the tempering circle. The temperature of the tempering medium in the tool changes depending on a tool temperature to a return temperature. The temperature difference between the feed temperature and the tool temperature can be positive or negative. With an increasing volume flow, the absolute value of the temperature difference is sinking.
A generic closed-loop control device is disclosed in the DE 43 05 772 A1. This document describes that the temperature difference between the feed temperature and the return temperature or the return temperature can be used as control value. The flow rate of the tempering medium is used as the actuation value.
In the case of this control device the fact is problematical that depending on the currently present flow rate of the tempering medium a small change of the flow rate can lead to a very strong or weak change of the temperature difference. Put in other words, the control behavior (control quality), this means the transient response of the control value in the case of changes of the target value or in the case of disruptions, depends on the currently present operating point. If there is an operating point in the case of which a small change of the flow rate leads to a small change of the temperature difference, the closed-loop control device shows a slow transient response. If there is an operating point in the case of which a small change of the flow rate leads to a high change of the temperature difference, the closed-loop control device shows a fast transient response or can become unstable. This hampers a stable controlling of the at least one control value (here the return temperature or the temperature difference between the feed temperature and the return temperature).
In the case of known molding machines it was mostly necessary to newly parameterize the closed-loop control device as soon as a new tool was mounted or other changes concerning the tool were made or when target value changes or operating point changes have occurred.